The invention relates to a method for repairing a damaged site in the surface of a cast part, in which method a repair material is applied to the damaged site by cold gas spraying. The invention moreover relates to a method for producing a repair material for a component.
Cold gas spraying is a process which is known per se, in which particles intended for the coating are accelerated, preferably to supersonic speed, by a convergent-divergent nozzle, so that they remain adhering to the surface to be coated on account of their impressed kinetic energy. In this respect, the kinetic energy of the particles is utilized, leading to plastic deformation thereof, with the coating particles being melted merely at their surface during impingement. Therefore, this process, compared to other thermal spraying processes, is referred to as cold gas spraying because it is carried out at relatively low temperatures, at which the coating particles remain substantially solid. A cold gas spraying plant having a gas heating device for heating a gas is preferably used for the cold gas spraying, which is also termed kinetic spraying. A stagnation chamber is connected to the gas heating device and, at the outlet side, is connected to the convergent-divergent nozzle, preferably a Laval nozzle. Convergent-divergent nozzles have a convergent partial portion and also a divergent partial portion, these being connected by a nozzle neck. At the outlet, the convergent-divergent nozzle generates a powder jet in the form of a gas stream with particles located therein at high speed, preferably supersonic speed.
According to EP 1 816 235 B1, it is known that imperfections in cast parts can be repaired by cold gas spraying. For this purpose, use is made of materials which are designated as homogeneous as per EP 1 816 235 B1. This is to be understood as meaning materials which have a similar composition to or the same composition as the component to be repaired. This can have the effect that the repaired site is filled with a material which virtually completely precludes metallurgical problems. This means that it is possible to preclude diffusion processes, which arise after a repair has been made to a cast part using a material of a different type, particularly in the case of components subject to high thermal loading, and lead to a reduction in the integrity of the microstructure. Specifically, in the worst case these can lead to component failure.
However, the homogeneous material for repairing the imperfections in the cast part forms a microstructure which, in terms of its microstructure, is different from the cast microstructure of the surrounding component.